POSSIBLE MECHANISM OF SUPPRESSION OF THE GROWTH OF FUSARIUM-OXYSPORUMF-SP RAPHANI BY NITRATE IN SOIL

A possible mechanism of suppression of the growth of Fusarium oxysporu m f. sp. raphani by nitrate was studied. High concentration of nitrate in soil suppressed the population of F. oxysporum f. sp. raphani, and the effect of nitrate was more pronounced in the soil with a higher C a content. In the medium, nitrate (as KNO3) inhibited the conidial for mation of the fungus, while the mycelial growth of the fungus was not inhibited at a concentration of nitrate up to 200 mg NO3-N/L. The surv ival of the conidia decreased with increasing nitrate level in the soi ls of both the rhizosphere and non-rhizosphere. The chlamydospore form ation was stimulated by the nitrate amendment. The presence of large n umbers of Fusarium-antagonists, actinomycetes and bacteria, in the nit rate-amended soil was also considered to contribute to the reduction o f the population of F. oxysporum f. sp. raphani.